1. Field of the Invention
The present invention concerns a process for centrifugal separation of materials contained in a liquid slurry. More specifically, the invention concerns such a process wherein the slurry includes a light material having a specific gravity that is less than the liquid carrier and a heavy material having a specific gravity that is greater than the liquid carrier. A gas, preferably air, is injected into the slurry prior to feeding the slurry to a hydrocyclone, resulting in an enhanced degree of separation of the light and heavy materials.
2. Description of Related Art
Hydrocyclones have been employed for many years to separate solid materials of differing specific gravity from liquid slurries. Separation of light particles from slurries has been enhanced in the past by adjusting the specific gravity of the liquid carrier by addition of salts. However, this results in increased cost and environmental concerns.
In the paper industry, a variety of reverse centrifugal cleaning methods have been used to remove good paper fibers from contaminants of closely similar or lower specific gravities. A discussion of reverse centrifugal cleaning is provided in Seifert et al., U.S. Pat. No. 4,155,839 and Bliss U.S. Pat. No. 4,565,443.
It has been found that enhanced separation of light and heavy particles from a slurry containing light particles having a specific gravity that is less than the liquid carrier and heavy particles having a specific gravity that is greater than the liquid carrier is achieved by injection of air into the slurry upstream of the hydrocyclone. The process does not require modification of the hydrocyclone apparatus and, as a result of the increased efficiency of separation of the heavy and light components, reduces the number of passes required to achieve a high degree of separation.